1. Field of the Invention
The present invention relates to a sheet supplying apparatus used with an image forming apparatus such as a copying machine, a printer, a facsimile machine and the like.
2. Related Background Art
In general, in a sheet supplying apparatus for an image forming apparatus such as a copying machine and the like, a plurality of sheets such as transfer sheets, photosensitive sheets or the like is stacked on a sheet stacking plate (movable plate) 101 in a sheet supply cassette 100 as shown in FIG. 24, and the sheets are supplied from the sheet stacking plate 101 and are separated one by one by a sheet supply means such as a sheet supply roller to be fed to a next station.
However, in such a sheet supplying apparatus, in the sheet supply cassette 100 acting as a sheet containing portion, a free end portion of the sheet stacking plate 101, normally biased upwardly by a biasing spring 102, or a front end portion of the sheet stack rested on the sheet stacking plate 101, is pushed upwardly toward an uppermost position so that the sheet stack is abutted against the separating claws 103 or the sheet supply means stably. Accordingly, the replenishment of new sheets into the cassette 100 must be effected while pushing down the sheet stack plate 101 in opposition to the biasing force of the biasing spring 102 and keeping the front ends of the sheets from a separation means and the sheet supply means, thereby worsening the workability of the replenishing operation.
To eliminate such inconvenience, recently, a sheet supplying apparatus as shown in FIG. 25 has been proposed (refer to the Japanese Utility Model Publication No. 52-53225).
In this sheet supply apparatus, a cassette 105 is provided with a locking means 109 (comprising a pin 110 formed on a sheet stacking plate 106 and a lock lever 112 attached to a side plate 111 of the cassette 105) for locking the sheet stacking plate 106 at a predetermined position when the sheet stacking plate 106 is pushed down in opposition to a biasing spring 107. After the sheets are replenished into the cassette 105, when the cassette 105 is mounted to an image forming apparatus (not shown), the lock of locking means 109 (locking lever 112) is released by a releasing means 113 of the image forming apparatus. When the cassette is mounted to the image forming apparatus, the releasing means 113 drives the lock lever 112 in a counterclockwise direction, thereby releasing the lock lever 112 from the pin 110.
Incidentally, in FIG. 25, the reference numeral 106A denotes a pivot pin for the sheet stacking plate 106; 112A denotes a pivot pin for the lock lever 112; 115 denotes a biasing spring for the lock lever 112; 116 denotes a separating claw; and 117 denotes a sheet supply roller.
However, in the above-mentioned sheet supplying apparatus (FIG. 25), as the cassette 105 is mounted to the image forming apparatus, when the locking means 109 is released by the releasing means 113, the sheet stacking plate 106 suddenly spring back by the action of the biasing spring 107, thereby frightening the operator, causing damage of the sheets from collision between the sheets and the separation means 117 and/or the sheet supply means 117 and from the jamming of the sheets due to the deviation of the stacking position, and causing trouble in the image forming apparatus due to the shock to the image forming apparatus. This is noticeable particularly when the cassette 105 containing a small amount of sheets in comparison with the capacity of the cassette is mounted to the image forming apparatus, as in the case where jam treatment is effected or a small amount of sheets having low frequency of use are used temporarily.